STORY ARCHIVE

Oyster Killer

The delicious Sydney Rock Oyster is under threat from a mysterious killer that seems to strike at random. This forensic mystery story follows a team of scientists on the trail of the deadly QX disease. They’re puzzled about why the disease is occurring randomly in oyster beds along the east coast of Australia. In some areas over 80% of the oysters have died because of this mysterious disease. With a $30 million dollar business under threat, it’s a race against time to stop oysters disappearing off the menu. But, science is coming to the rescue in, and finally coming up with some solutions.

TRANSCRIPT

Narration: Bob Drake is a 4th generation oyster farmer on the Georges River, south of Sydney.

Bob Drake: Love the river, my dad’s grandfather started the oyster scene that we’ve got now. Dad worked all his life in it. Me and my two brothers have had a great time with it up until 1995.

Narration: 1995 was the year a mysterious oyster disease called Qx put an end to Bob’s oyster-farming dynasty. Now the government pays Bob and his brothers to pull up the old, abandoned oyster leases.

Bob Drake: Its devastating to see what’s happening to families to see the changes and the moves they’ve had to make, they’re all backward steps. This lease here behind me probably grew about $50,000 worth of oysters a year. Qx slaughtered their crop and they lost their leases, lost their vessels, lost the works.

Narration: Qx is a disease that strikes at random. Nobody knows why it can wipe out oysters in one estuary and leave others untouched. This is the story of a team of scientists who’ve been battling to understand this mystery disease and how to stop it.

At stake is a $30-million-a-year industry.

Originally it was described in Queensland as a Q. X is a generic mystery. So prior to the 1970's it was a mystery organism. Rob Adlard has been working on the QX bacterium for nearly 10 years. He now knows how QX kills.

Rob Adlard: So you will see a whole heap of oyster cell nuclei around quite a lot of this pink material oyster cells. But you can see quite easily these spores have QX disease. The two dark blobs are the spores and the spherical bottoms are associated with the pathogen.

Paul Willis: So whereabouts in the oyster does the QX sit?

Rob Adlard: What it seems to do is take out the digestive gland, and effectively the oyster starves to death because it can’t then process its food.

Narration: Knowing the enemy was just the first step. The next piece of the puzzle was to understand how it spreads. For years QX had been a relatively unimportant problem. It doesn’t affect humans and it had only struck a few small oyster fisheries in southern Queensland and northern New South Wales. But 1995 changed all that. QX jumped over 500 kilometres south to the Georges River in the heart of Sydney. It took just five years to wipe out the largest and oldest Sydney Rock oyster fishery.

Bob Drake: It’s an absolute horror to us, I just don’t know why Georges River was picked to suffer this great blow.

Narration: It looked like QX could strike anywhere, without warning. As fear gripped oyster farmers up and down the coast the next scientist joined the battle. Dave Raftos is an immunologist. He had to find out why QX had affected some estuaries, but left others un touched. He looked at a crucial component of the oyster’s immune system, an enzyme called phenyl oxidase. A healthy immune system has plenty of it. He compared phenyloxidase in oysters from the infected Georges river with oysters from the unaffected Hawkesbury River.

Dr Dave Raftos: In the Hawkesbury River, which has never been affected by QX disease, phenyloxidase activity is much higher than it is in oysters from the heavily QX infected Georges River

Narration: So was it something wrong with the oysters or something about the rivers? To find out Dave took healthy Hawkesbury River oysters and put them into the Georges River.

Dr Dave Raftos: Remarkable things happened remarkably quickly. Within five days of transferring an oyster from the Hawkesbury into the Georges River, phenyloxidase activity starts going through the floor, it really does decrease very rapidly. The other interesting thing is that we find infection by the parasite that causes QX disease very shortly after that.

Narration: It was a crucial find. Something was destroying the oyster’s immune system, before QX could attack.

Dr Dave Raftos: Our data certainly shows that the immune system of oysters in these effected areas is suppressed but we don’t know why.

Narration: Meanwhile Rob Adlard had found something even more worrying. QX was turning up in more and more estuaries, but the oysters weren’t dying, at least not yet.

Rob Adlard: We picked up the four estuaries where we expected the disease to occur, but we also picked up 11 estuaries where the disease agent has never been reported and in those estuaries, the agent hadn’t progressed to a disease.

Paul Willis: So it’s present but it’s not causing a disease?

Rob Adlard: That’s how it appears at the moment.

Narration: QX could be a time bomb ticking away. It’s more wide spread than previously thought, and still the scientists have no idea what causes the immune collapse in oysters allowing QX to turn deadly. In the war against QX, it’s time to strike out in a different direction altogether. The New South Wales Department of Fisheries has begun a counter attack. They’ve set out to create a QX resistant Sydney Rock Oyster. They rounded up the few oysters in the Georges River that had survived the QX attack. Assuming that they had some natural resistance to the disease, the Fisheries began to cross breed these survivors to spread and strengthen their natural resistance. It was assisted natural selection in the quest to breed a Super Oyster.

Dr Steve Kinelli: This is some of our replicate trays that we're running our selected breeding program in. We anticipate around well so far two generations… we were getting sixty percent mortality. Eventually we hope at this rate within about eight years or so at this rate of improvement each generation will be able to have an oyster that’s fairly resistant to QX disease. The amazing thing is, when Dave Raftos took a closer look, to his surprise the improved oysters were loaded with phenyloxidase, the signature of a healthy immune system.

Dr Dave Raftos: And we think what's happening is that the new version of this phenyloxidase gene that you find in resistant oysters isn’t susceptible to being suppressed like you find in areas where there are QX disease outbreaks.

Narration: So, for the first time in the war against QX, there’s some light at the end of the tunnel. A QX resistant super oyster with a beefed up immune system is on its way. But the good news has come too late for oyster farmers like Bob Drake.

Bob Drake: Well for me… well I feel that at 64 years of age I am a little bit too late to set up elsewhere and I'll probably see my time out here messing round on Georges River and Botany Bay and we've got a great affiliation and I feel like staying here.